1. Field of the Invention
The present invention relates generally to a gas laser device, and more particularly, to a gas laser device including a discharge tube shaped for increased oscillation efficiency.
2. Description of the Related Art
Increasing the oscillation efficiency in gas laser devices is an important technical target. Techniques for achieving this target include the generation of positive discharge resistance characteristics due to electron capture in a high-frequency electric discharge, and the removal of a cathode effect. The electron capture technique requires increasing the frequency of an electric discharge power supply.
It is highly difficult to provide a high-output, high-frequency power supply. In order to achieve electron capture, i.e., to prevent electrons from reaching side walls of a discharge tube, it is necessary that the distance d between electrodes in the discharge tube be considerably greater than the distance l that electrons move per half of the frequency, as indicated by the following equation: EQU l=2 .mu.E/.omega.=Ve/.pi.f&lt;&lt;d
where
l--the distance which electrons move, PA1 .mu.--electron mobility, PA1 E--electric field intensity, PA1 .omega.--angular velocity of the power supply, PA1 f--frequency of the power supply, PA1 Ve--speed of electrons, about 8.times.10.sup.6 cm/sec, and PA1 d--distance between side walls of the discharge tube.
Assuming that d=2 cm and the minimum distance for the electrons not to collide with the side walls is l=d, f is calculated as follows: EQU f=1.24 MHz.
Therefore, a considerably high frequency is required.
Vacuum tubes may be employed in a high-frequency power supply. However, since the service life of vacuum tubes is only about 3,000 hours, it would be problematic to construct a practical gas laser device employing such a high-frequency power supply. Therefore, solid-state devices such as semiconductors or the like should desirably be employed to construct a high-frequency power supply. In a large-output range, however, the output frequency of a currently available high-frequency power supply constructed of solid-state devices is about 2 MHz. Thus, the above requirement cannot be satisfactorily met. Specifically, assuming that the frequency of a high-frequency power supply is 2 MHz, then EQU l/d=0.62.